doc: Change optional metadata types default to an empty list

Connected with changes in libdnf and based on the https://fedoraproject.org/wiki/Changes/DNFConditionalFilelists.

doc/conf_ref.rst

@@ -433,10 +433,7 @@ configuration file by your distribution to override the DNF defaults.
 
  Note that the list can be extended by individual commands to explicitly request loading specific metadata type.
 
- Currently only ``filelists`` value is supported. Default is ``filelists``.
-
-..
- # TODO(jkolarik): Change the default to an empty list when dropping the filelists for Fedora 40
+ Currently only ``filelists`` value is supported. Default is an empty list.
 
 .. _persistdir-label: